This invention concerns a defibrator for manufacturing a fibrous product preferably of cellulosic fibers by separating a sheet of raw material by means of rotating beater bars provided in a cylindrical housing and cooperating with a stationary beater plate provided adjacent an inlet opening through which the sheet of raw material is introduced into the cylindrical housing, wherein the axis of rotation of the beater bars is off-set in relation to the central axis of the cylindrical housing.
The fibers to be used in the present invention comprise cellulosic fibers, wood fibers, mixtures with synthetic fibers including bicomponent fibers and synthetic fibers. The synthetic fibers may, e.g., be of polypropylene or polyethylene. Also glass fibers, rock wool fibers, and pretreated fibers may be used.
The defibrator according to the present invention makes it possible to effect a good defibration, and accordingly, there is no need to use a distributor. The defibrated fibers may be deposited directly from a discharge opening of the defibrator.
When dry forming a paper it is customary to connect a defibrator used for defibrating the sheets of raw material with a specific distributor. The distributor makes it possible to distribute the fibers. Besides, a distributor makes it possible to catch any agglomerations of fibers which may detoriate the fibrous web formed. With the art it is well-known that such agglomerations of fibers are always found in the discharge from prior art defibrators.
Provided that the defibrator may effect a defibration so that no agglomerates of fibers or substantially no agglomerates occur in the discharge from the defibrator. A distributor will not be necessary for a great number of products
It is an object of the present invention to provide a defibrator having improved defibration.
It is a further object of the invention to provide a defibrator making it possible to discharge fibers directly onto a forming wire, thereby obviating the need of using a distributor at least when making products wherein it is accepted to have agglomerates comprising a few, e.g., 2-5, interconnected cellulosic fibers.
It is a further object of the invention to provide a defibrator having a discharge opening with a length corresponding to the width of the product to be formed on the forming wire.
According to the present invention the above objects are obtained with a defibrator wherein the axis of rotation of the beater bars is off-set in relation to the central axis of the cylindrical housing, wherein the inner surface of the cylindrical housing of the defibrator is provided with ribs having a surface facing against the axis of rotation with a curvature for directing the fibers into the working area of the beater bars, the ribs are arranged adjacent the inlet opening in direction of rotation for the beater bars, and wherein the outlet opening is covered with a grate formed by parallel grate bars, each grate bar extends in a plane perpendicular to the axis of rotation and has a curved surface arranged in a distance from the axis of rotation corresponding to the distance between the axis of rotation and the outer edge of the beater bars, thereby making it possible to clean the grate by means of the rotating beater bars.
The action of the beater bars is not a cutting. The beater bars effect rather a breaking of the raw material in order to separate it into individual fibers. In order to obtain a secure separation into individual fibers the beater bars should act on the fibers or agglomerations of fibers as many times as possible. This is achieved in the defibrator as the surfaces of the ribs direct agglomerates of fibers into the working area of the beater bars.
The use of ribs having curved surfaces makes it possible to direct fibers into the working area of the rotating beater bars. Due to the higher mass of an agglomeration of fibers such agglomeration will be directed or thrown into the working area of the beater bars with a greater force than the single fibers. Accordingly, it is possible for the beater bars to act on the fibers, several times, whereby a very secure defibration of the fibers is obtained.
An agglomeration of fibers which is retained by the grate will also be thrown into the working area of beater bars when the outer edge of the beater bars pass the grate. Thus, such agglomeration will be subjected to further action from the beater bars, whereby a better defibration is obtained.
It is preferred that the grate bars taper in the direction of the flow in order to hinder the fibers in being caught in the interspace between adjacent grate bars.
Inside the cylindrical housing a banana-shaped area is provided due to the excentricity. In this area the beater bars are not active. The fibers provided in this area will be single fibers. Even though it might be advantageous to have the outlet opening arranged in this part of the cylindrical wall, it is preferred to have the outlet opening arranged in an area in which the beater bars operate. Thereby it is possible to use the beater bars as cleaning members for the grate arranged in the outlet opening.
Moreover, it is preferred to arrange a suction fan in the outlet of the defibrator in a position between the outlet opening and the discharge opening. Such suction fan will ensure a more even distribution of fibers. However, it might also be possible to provide the distributor without a suction fan. In this case an air flow is provided by a suction box arranged at the opposite side of a forming wire.
According to a preferred embodiment the sheet of raw material is introduced substantially horizontal in a 3 o'clock position and the beater bars are rotated counter clockwise. In such defibrator the outlet opening is arranged in a 6 o'clock position. This ensures that the fibers pass through at least 270.degree. whereby the beater bars might act several times on each fiber.
Further features and advantages of the present invention will be understood by reference to the attached drawings taken in conjunction with the ensuing discussion.